Try GE or RCA tubes in the RP-7. I liked them better than the much more expensive Millard’s. The RP-7 is a wonderful match with solid state power amp.
New Rogue RP-7 Preamp
I just ordered a Rogue RP-7, arriving in about 2 weeks. My plan is to use it with a new Bryston cubed amp. I've never actually heard this pairing, but have read elsewhere that this is a good sonic match. My goal is to add just a bit of the tube sound to the system, although it's said that this pre rides the line between SS and tube sound. In any case, just to take a bit of the SS edge off. This pre is also to replace an AR LS17SE that I really like, but it's time to try something new and the Rogue fits the bill for now.
I'd love to hear any comments or experience with this pairing from the folks here. Thanks.